The colouring of hair has become increasingly popular in recent years, and many different colouring systems have been developed for use in this context. There are generally three types of hair colouring system in widespread use: permanent, semi-permanent, or temporary.
Technology for permanent hair colorants has advanced significantly over the past decade. Consumers can achieve vibrant and multi-dimensional colour from these products and consequently have high expectations. It is particularly important that the colour maintains its vibrancy, intensity and original hue during normal wear. Colour fading can be initiated by environmental circumstances, such as by UV exposure. However the washing process is the most significant factor in the removal of hair colour. Some colouring components are more easily washed out during shampooing or rinse-off conditioner application, and this “washing-out” causes both fading and change of tone. In particular this is observed with red shades. Other sensory characteristics such as shine, body, lustrous feel and manageability are also linked to colour retention.
For this reason, specialized shampoos and conditioners have been designed specifically for hair treated with permanent colorants. For example, certain families of silicones such as amodimethicone and derivatives have been described as a colour-lock aid in rinse-off hair care products. WO2009/085838 describes a hair colour protection technology based upon the application of hydrophobically modified cationic polymers such as Polyquaternium-55. This is said to be most effective when formulated in a 3-step anti-fading system comprising shampoo, conditioner and leave-in treatment or styler.
A problem associated with hair colour protection technologies is that is difficult to evaluate their effectiveness. Current methodologies for assessing the hair colour changes which are attributable to “washing-out” tend to give hugely variable results. Often they are not sufficiently sensitive or differentiating, which makes it impossible for the tester to compare different technologies in terms of effectiveness.
The present invention provides a solution to this problem.